This research will determine the mechanisms by which the fungicides benomyl and carbendazim induce testicular atrophy. Benomyl is a systemic benzimidazole fungicide that is used widely on numerous food crops and ornamentals. Carbendazim, also a benzimidazole fungicide, is a metabolite and natural breakdown product of benomyl. Both of these chemicals are known male reproductive toxicants. Benzimidazole exposures induce focal and total testicular atrophy, which cause infertility in male rats. However, the mechanisms leading to infertility remain unknown. Preliminary studies indicate that occlusion of the efferent ductules of the testis may be a major factor in the development of testicular atrophy. The proposed experiments will determine: a. acute dose-dependent changes in the testis and efferent ductules after exposure to benomyl and carbendazim; b. whether carbendazim's acute effects on the testis and efferent ductules are independent; c. the effect of carbendazim on Sertoli cell morphology in the testis; d. whether carbendazim disrupts the structure and function of ciliated and nonciliated cells of the ductal epithelium; e. if the testicular injury is reversible, depending upon the extent of efferent ductule or seminiferous tubule damage; and f. the relationship of testicular and ductal damage multiple exposures to low dosages of carbendazim. The results of this research will provide valuable information regarding the mechanisms of male infertility produced by the benzimidazole class of compounds, which will allow for more informed decisions of occupational risk to males from the wide spread use of these fungicides.